ibm_newemac: emac_close() needs to call netif_carrier_off()

When ibm_newemac netdev instance is shutdown with "ifconfig down",
the netdev interface does not go properly down. netif_carrier_ok()
keeps returning TRUE even after "ifconfig down".

The problem can be seen when ibm_newemac instances are slaves of
a bonding interface. The bonding interface code uses netif_carrier_ok()
to determine the link status of its slaves. When ibm_newemac slave is
shutdown with "ifconfig down", the bonding interface won't detect any
link status change because netif_carrier_ok() keeps returning TRUE.

Signed-off-by: Petri Gynther <pgynther@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>